[jira] [Created] (FLINK-4241) Cryptic expression parser exceptions

[Till Rohrmann (JIRA)]

Till Rohrmann created FLINK-4241:
------------------------------------

             Summary: Cryptic expression parser exceptions
                 Key: FLINK-4241
                 URL: https://issues.apache.org/jira/browse/FLINK-4241
             Project: Flink
          Issue Type: Improvement
          Components: Table API & SQL
    Affects Versions: 1.1.0
            Reporter: Till Rohrmann


The exceptions thrown when giving wrong SQL syntax to Flink's SQL parser is 
very cryptic and should be improved. For example, the following code snippet:

{code}
inputTable.filter("a == 0");
{code}

gives the following exception:

{code}
Exception in thread "main" 
org.apache.flink.api.table.ExpressionParserException: Could not parse 
expression: [1.4] failure: `-' expected but `=' found

a == 0
   ^
        at 
org.apache.flink.api.table.expressions.ExpressionParser$.parseExpression(ExpressionParser.scala:355)
        at org.apache.flink.api.table.Table.filter(table.scala:161)
        at 
com.dataartisans.streaming.SimpleTableAPIJob.main(SimpleTableAPIJob.java:32)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
{code}

>From this description it is very hard to understand that {{==}} is not a valid 
>operator.

I think it would considerably improve user experience if we print more helpful 
parsing exceptions.





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